俱舍論頌疏論本 2.104

2.104

釋曰：五外二所識者，色等五境名為五外，此外五境二識所識：一為五識所識、二為意識所識。除此五界，餘十三界義准應知。唯意識識、非五識身所緣境故。

The explanation says: 'The five external are cognized by two': the five objects, form and the like, are called the five external [elements]. These five external objects are cognized by two consciousnesses: first, they are cognized by the five consciousnesses; second, they are cognized by the mental consciousness. Excluding these five elements, the remaining thirteen elements should be understood by implication to be cognized solely by the mental consciousness, because they are not objects of the collection of the five consciousnesses.